The present invention relates generally to magnetic resonance spectroscopy (MRS) and, more particularly, to a system and method for multiple-receivcr proton spectroscopy such that a single absorption spectrum is generated as a combination of data received from multiple receiver coils.
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, Mz, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received and processed to form an image or a magnetic resonance spectroscopy.
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals is digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
Magnetic Resonance Spectroscopy (MRS) may be used in vivo for the determination of individual chemical compounds located within a volume of interest. The underlying principle of MRS is that atomic nuclei are surrounded by a cloud of electrons which slightly shield the nucleus from any external magnetic field. As the structure of the electron cloud is specific to an individual molecule or compound, the magnitude of this screening effect is then also a characteristic of the chemical environment of individual nuclei. Since the resonant frequency of the nuclei is proportional to the magnetic field it experiences, the resonant frequency can be determined not only by the external applied field, but also by the small field shift generated by the electron cloud. Detection of this chemical shift, which is usually expressed as “parts per million” (PPM) of the main frequency, requires high levels of homogeneity of the main magnetic field Be.
Typically, MR proton spectroscopy is used to generate a one-dimensional (1D) frequency spectrum representing the presence of certain chemical bonds in the region of interest. In medical diagnosis and treatment, MRS provides a non-invasive means of identifying and quantifying metabolites from a region of interest, often the human brain. By finding the relative spectral amplitudes resulting from frequency components of different molecules, medical professionals can identify metabolites indicative of diseases, disorders, and other pathologies such as Alzheimer's disease, cancer, stroke, and the like. In this context, two nuclei are typically of particular interest, HR and p31. Phosphorus 31 MRS is directed to the detection of compounds involved in energy metabolism relating to membrane synthesis and degradation. Metabolites of particular interest in proton MRS studies include glutamate (Glu), glutainine (Gln), choline (Cho), creatine (Cre), N-acetylaspartate (NAA), and the inositols (mI and sI).
Recently, increased sampling resolutions and the ability to simultaneously receive data from multiple-channel receiver coils has lead to greater accuracy in MR data acquisition. Accordingly, radiologists and other medical personnel are able to review separate MRS results from each channel for data acquired during a single scan. Additionally, improved data acquisition capabilities have created opportunities for implementing new signal processing algorithms to improve the sensitivity and accuracy of MRS procedures. Specifically, nonparametric techniques, such as Capon analysis and Amplitude and Phase Estimation of a Sinusoid (APES) analysis can provide 2D results for MRS experiments that show both frequency and damping information. These techniques provide improved sensitivity and differentiation between metabolites.
However, whether implementing 1D or 2D proton spectroscopy, interpreting the results of multiple channels can be a tedious and time consuming process because a medical professional must inspect the results from each channel independently. That is, since a separate result for each channel is generated, when reviewing the results, the medical professional must independently interpret the results from each channel. This process of reviewing multiple sets of results and changing therebetween creates an arduous review process that is susceptible to erroneous human estimations and decreases patient throughput. That is, since the medical professional reviewing the results must repeatedly switch between the results from each independent channel, the medical professional is required to estimate an overall review of data acquired from the various independent channels. For example in an 8 channel head coil, a medical professional must individually review data from 8 different receiver channels to make a diagnosis. Relying on human estimation not only lengthens the review process but also complicates the diagnostic process.
It would therefore be desirable to have a system and method capable of generating a single set of results from a multiple receiver MR proton spectroscopy scan.